One of the outstanding challenges in the environmental area is the cleanup of water generally. Legislation in various countries has paid increasing attention to permissible levels of impurities in water, especially where the stream may ultimately be used as a water source for human consumption. A class of impurities commonly found in streams is the class of metal ions, some of which may have long-term deleterious effects on life generally and on humans in particular. Thus, much attention has been paid to the removal of metal ions generally from aqueous streams.
Several methods have been used for metal ion removal. One general procedure has been to form insoluble compounds from metallic ions dissolved in aqueous streams and then either removing these directly by filtration, or agglomerating or flocculating the insoluble compounds as a filtration or settling aid. Another approach is to remove metallic ions by treating aqueous streams with an ion exchange resin. Yet another approach has been to remove metal ions using an adsorbent such as alumina or, even more frequently, carbon in one or another of its forms.
Several years ago there was described a class of materials characterized as carbonaceous pyropolymers possessing recurring units containing at least carbon and hydrogen atoms on the surface of the material. See U.S. Pat. Nos. 4,329,260; 4,471,072; 4,499,201; 4,536,358. These carbonaceous pyropolymers were said to have some adsorbent properties, which is not surprising in view of their relatively large surface area and porous nature. Although the carbonaceous pyropolymers superficially are related to various adsorptive carbons it also is clear that the carbonaceous pyropolymers are distinct from the latter, especially in having recurring units of carbon and hydrogen atoms on the surface of the material.
What we have found is that the carbonaceous pyropolymers described in the prior art are effective in removing metallic ions from aqueous solutions. Their effect is not indiscriminate; in fact the carbonaceous pyropolymers are quite specific with respect to the metal ions which are removed, and their specificity is itself quite unusual and different from anything in the prior art. In fact, the carbonaceous pyropolymers are effective in removing from aqueous solutions those metal cations which have a reduction potential relative to the zerovalent state of greater than about -0.2 volts. We believe this requirement arises because the carbonaceous pyropolymers remove metal ions not by adsorption, but rather by reducing the metal ions to their zerovalent state with concurrent plating of the metal onto the carbonaceous pyropolymer. Not only is removal of metal ions specific, but where they are effective the carbonaceous pyropolymers act rather quickly and are readily capable of reducing the concentration of some metal cations more than 1,000-fold.